Competition ski boats normally have a powerful (i.e., 250-400HP and above) inboard engine mounted in a mid-travel position. That is, the engine is located directly behind the driver and front passenger seats in a hump mostly above the floor of the boat. Mounting the engine in the mid-travel position leaves room available rearward of the engine near the transom of the boat for passengers to maneuver when attending water-skiers. In such a system, it is typical that the engine, the transmission, and the propeller shaft are mounted in-line at a downward angle of about 12 degrees to the hull of the boat, such that the propeller shaft exits rearward through the hull at the 12 degree angle.
A propeller is rotated by the propeller shaft, and because of the 12 degree downward angle, the propeller not only thrusts the boat forward, but also pushes in part upward on the boat so that the boat can be lifted to plane quicker. It is useful for the propeller to be located forward of the transom underneath the hull of the boat to reduce turbulence behind the boat. Steering in such a system is normally accomplished using one or more rudders attached to the transom.
The transmission receives an engine crankshaft, and the propeller shaft is coupled to the other end of the transmission by a transmission coupler. The engine and the transmission are mounted to joists or studs located in a hull space of the boat, which is in between the hull and the floor of the boat. It is extremely important that mounts for the engine and the transmission be strong and adjustable. Strength and adjustability are important because the crankshaft of the engine, the transmission, and the propeller shaft must remain in line even when subjected to extreme forces. Extreme forces on the mounts are possible because ski boats have high power requirements both at start up and when operating at high speeds.
As noted above, the engine is located in a hump behind the driver and front passenger seats when the engine and transmission are mounted in the mid-travel position. It is desirable to reduce the size of the engine hump without reducing the performance and power capacities of the engine.